Organic electronic devices generally refer to devices in which when charges are injected into an organic layer disposed between an anode and a cathode, phenomena occur, such as light emission or electricity flow. The functions of the devices are determined depending on what kind of organic material is selected.
Organic light emitting devices (OLEDs) are representative organic electronic devices and have received attention as next-generation flat panel displays due to their thin thickness, light weight, and good color representation. Organic light emitting devices can be fabricated on existing inorganic substrates, including glass substrates and silicon substrates, metal substrates, and flexible substrates, such as plastic substrates and metal foils. Due to their high sensitivity to water and oxygen, organic electronic devices tend to lose their luminous efficiency and lifetime when exposed to ambient air or when water enters the panels from the outside.
As solutions to the above problems, attempts have been made to block water and oxygen from entering from the outside by the use of glass caps or metal caps, the use of laminated encapsulation films or the deposition of inorganic materials. Another method has been proposed to achieve good adhesiveness and hermetic sealing by applying a curable film or material to the surface of an organic layer or metal layer and curing the curable film or material.
However, susceptibility of glass caps to mechanical damage makes it difficult to fabricate organic electronic devices over a large area, differences in the coefficient of thermal expansion between metal caps and substrates are problematic in terms of processing, and water and oxygen enter laminated adhesive films through the interface between the adhered film layers. A process is known in which organic materials are deposited under vacuum and inorganic materials are sputtered under vacuum. According to this process, inorganic materials should be deposited to form a multilayer structure by vacuum sputtering in order to prevent the ingress of water and oxygen through the upper interface of the sputtered structure, leading to low productivity, and the formation of the multilayer structure of organic materials and inorganic materials under vacuum is an obstacle to large-scale production.
Liquid encapsulation methods have the disadvantage that by-products formed by cleavage of chemical bonds and in the course of curing or unreacted curing initiators remain in sealed structures, impeding the driving of organic electronic devices or shortening the lifetime of organic electronic devices. For example, Korean Patent Publication No. 2002-0090851 discloses an organic light emitting device that has a barrier film consisting of one or more layers on a light emitting element to block water from entering wherein the barrier film is formed by laminating a dry film photoresist or applying and curing a transparent photosensitizer.
The barrier film formed of the dry film photoresist or the liquid photosensitizer can function to block external environmental factors, such as oxygen or water, from entering the organic light emitting device but contains inevitable impurities from the chemical composition, such as by-products formed during curing and an unreacted initiator. Such residues remain unremoved from the device and enter the organic layer or metal layer, impeding the driving of the device or shortening lifetime of the device.
Many devices undergo degradation by the ingress of oxygen and water in air and chemical gases or liquids used during fabrication of the devices. Encapsulation is applied to protect devices from such degradation. Various types of encapsulated devices are known. For example, U.S. Pat. No. 6,573,652 describes encapsulated liquid crystal displays, light emitting diodes, light emitting polymers, electroluminescent devices, and phosphorescent devices. Further, U.S. Pat. No. 6,548,912 describes encapsulated microelectronic devices, including integrated circuits, charge coupled devices, light emitting diodes, light emitting polymers, organic light emitting devices, metal sensor pads, micro-disk lasers, electrochromic devices, photochromic devices, and solar cells. Particularly, WO 2007/025140 relating to an encapsulated device and a fabrication method thereof describes a method for encapsulating the device by forming a barrier stack including at least one barrier layer and at least one polymeric coupling layer adjacent to a substrate under high vacuum. This encapsulation method requires a process for forming a multilayer (5- to 7-layer) structure consisting of metal oxide layers as barrier layers and organic layers as polymeric coupling layers to block oxygen and water. The process is complicated and makes it difficult to apply the encapsulation method to large-area substrates and flexible substrates. Particularly, the application of the metal oxide layers requires a sputtering process using gas and an etching process. The additional processes increase the risk of damage to the polymeric coupling layers during processing, which is a cause of poor barrier properties.